Method for manufacturing probe sheet

ABSTRACT

An embodiment of the invention provides a method for manufacturing a probe sheet in which a probe tip can be arranged at a predetermined accurate position without the need for troublesome positional adjustment operations of the probe tip in coupling operations of each contactor and a probe sheet main body. It is a method for manufacturing a probe sheet comprising a probe sheet main body having conductive paths and a plurality of contactors formed to be protruded from one surface of the probe sheet main body and connected to the conductive paths. The manufacturing method comprises the steps of forming a plurality of the contactors on a base table by sequentially depositing on the base table metal materials for a plurality of contactors from their respective probe tips toward base portions with use of a photolithographic technique, forming on the base table the probe sheet main body to be coupled with the base portion of each contactor held on the base table, and separating the contactors from the base table integrally with the probe sheet main body.

PRIORITY CLAIM

The present application is a United States national phase applicationfiled pursuant to 35 USC §371 of International Patent Application SerialNo. PCT/JP2007/057358, entitled METHOD FOR MANUFACTURING PROBE SHEET,filed Mar. 27, 2007; which application claims priority to JapanesePatent Application Serial No. 2006-111814, filed Apr. 14, 2006; whichforegoing applications are incorporated herein by reference in theirentireties.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.12/296,430 entitled ELECTRICAL CONNECTING APPARATUS, filed Oct. 7, 2008,and U.S. application Ser. No. 12/297,214 entitled FLEXIBLE WIRING BOARDAND ELECTRICAL CONNECTING APPARATUS, filed Oct. 14, 2008 and applicationSer. No. 12/297,215 entitled PROBE SHEET AND ELECTRICAL CONNECTINGAPPARATUS, filed Oct. 14, 2008 and which are incorporated herein byreference in their entireties. Also this application is related to U.S.application Ser. No. 12/443,462 entitled ELECTRICAL CONNECTINGAPPARATUS, filed Mar. 27, 2009.

TECHNICAL FIELD

An embodiment of the present invention relates to a method formanufacturing a probe sheet suitable for use in an electrical test of aflat-plate-shaped device under test such as an integrated circuit or aboard for a display apparatus.

BACKGROUND

In a conventional electrical test of this kind, a probe sheet comprisinga probe sheet main body having a flexible insulating synthetic resinfilm and conductive paths supported by the synthetic resin film and aplurality of contactors formed to be protruded from one surface of theprobe sheet main body and connected to the conductive paths is usedbetween a tester main body and a device under test (e.g., refer toJapanese Patent Appln. Public Disclosure No. 2002-340932, incorporatedby reference).

Each contactor of the probe sheet is connected to an electrical circuitof the tester main body via the conductive path of the probe sheet mainbody. Also, the probe sheet is applied to the device under test so thatthe probe tip of each contactor contacts a corresponding electrode ofthe device under test. By the electrical contact with use of the probesheet, the device under test is connected to the tester main body.

Meanwhile, in such a probe sheet, the dimensional accuracy and thepositional accuracy of the probe tip of each contactor are major issuesin order to let the probe tips of the numerous contactors provided onthe probe sheet abut to the corresponding electrodes of the device undertest accurately.

Thus, in formation of such a probe sheet, each contactor is formed froma tip end as a probe tip toward a base end as a connection end to theprobe sheet main body in general (e.g., refer to Japanese Patent Appln.Public Disclosure No. 2003-43064 and Japanese Patent Appln. PublicDisclosure No. 2002-509604, which are incorporated herein by reference).After these contactors are respectively formed, they are coupled withthe probe sheet main body so that the respective base ends are connectedto the corresponding conductive paths of the probe sheet main body.

However, even if each contactor itself is formed highly accurately, itis not easy to fix each contactor to the probe sheet main body so thatthe probe tip of each contactor is located at a predetermined positionaccurately in operations to couple each contactor with the probe sheetmain body, and an error is easy to occur at the probe tip position ofeach contactor in these coupling operations. Also, to obtain an accurateprobe tip position, troublesome adjustment operations of the probe tipposition of each contactor may occur in the coupling operations of eachcontactor and the probe sheet main body.

SUMMARY

An embodiment of the present invention is a method for manufacturing aprobe sheet in which a probe tip can be arranged at a predeterminedaccurate position without the need for troublesome positional adjustmentoperations of the probe tip in coupling operations of each contactor anda probe sheet main body.

An embodiment of the present invention is basically a method formanufacturing a probe sheet comprising a probe sheet main body having aflexible insulating synthetic resin film and conductive paths supportedby the synthetic resin film and a plurality of contactors formed to beprotruded from one surface of the probe sheet main body and connected tothe conductive paths, and comprises the steps of forming a plurality ofthe contactors on a base table by sequentially depositing on the basetable metal materials for a plurality of contactors from theirrespective probe tips toward base portions with use of aphotolithographic technique, forming on the base table the probe sheetmain body to be coupled with the base portion of each contactor held onthe base table, and separating the contactors from the base tableintegrally with the probe sheet main body.

With the manufacturing method according to an embodiment of the presentinvention, the plural contactors formed at predetermined positions onthe base table are not separated individually, but the probe sheet mainbody to be coupled with the base portion of each contactor is formed onthe base table in a state where the probe tips of these contactors areheld at predetermined positions on the base table. Thus, each contactoris integrally coupled with the probe sheet main body during the processof forming the probe sheet main body in a state where its probe tip isheld at the predetermined position. Thereafter, the contactor isseparated from the base table integrally with the probe sheet main body.

As a result, conventional operations to couple the individual contactorswith the probe sheet main body are not needed, and associatedtroublesome positional adjustment operations of the probe tips of thecontactors are not needed. Accordingly, the probe sheet on which theprobe tip of each contactor is arranged accurately at a predeterminedposition can be manufactured more easily than in the conventional case.

A method for manufacturing a probe sheet according to an embodiment ofthe present invention is a method for manufacturing a probe sheetcomprising a probe sheet main body having a flexible insulatingsynthetic resin film and conductive paths supported by the syntheticresin film and a plurality of contactors formed to be protruded from onesurface of the probe sheet main body and connected to the conductivepaths, and comprises a first step of forming photoresist taking the formof each probe tip and each arm portion continuing into the probe tip ona base table having formed therein a recess for the probe tip of eachcontactor with use of a photolithographic technique and forming theprobe tip and the arm portion of the contactor by depositing a metalmaterial in the recess formed in the photoresist, a second step of,after removal of the photoresist, forming a sacrificial layer on the endportion of the arm portion and forming a first flexible synthetic resinlayer for the probe sheet main body on the sacrificial layer, a thirdstep of forming an opening reaching the arm portion via the flexiblesynthetic resin layer and the sacrificial layer, a fourth step offorming a base portion continuing into the arm portion of the contactorby depositing a metal material in the opening, and a fifth step offorming on the flexible synthetic resin layer photoresist taking theform of a conductive path passing on the base portion formed in theopening with use of a photolithographic technique and forming on thesynthetic resin layer the conductive path coupled with the base portionby depositing a metal material in a recess formed in the photoresist,wherein the contactors are separated from the base table integrally withthe probe sheet main body.

As the synthetic resin film or the flexible synthetic resin layer,polyimide may be raised representatively. Also, as the sacrificiallayer, a synthetic resin film referred to as a dry film may be used, forexample.

The base table may be a stainless steel plate. As the metal material forthe contactor, nickel or its alloy may be used. In this case, in thefirst step, prior to deposition of the metal material for the armportion on the base table, a nickel layer and a copper layer on thenickel layer may be sequentially laminated. The copper layer contributesto easy detachment of the arm portion from the base table. Also, thenickel layer acts to promote growth of the copper layer on the basetable. The metal material for formation of the arm portion may bedeposited on the base table via both the layers.

Deposition of the metal material for the arm portion and lamination ofthe nickel layer and the copper layer may be respectively conducted by aplating technique, and for the arm portion, an electroforming technique,which is one of the plating techniques, may be used.

In the first step, prior to deposition of the metal material for the armportion on the base table, a harder metal material than the metalmaterial for the arm portion may be deposited in the recess on the basetable, and after deposition of the metal material, the metal materialfor the arm portion may be deposited to cover the metal material. Thedeposition of the hard metal material enables to form the probe tip ofeach contactor with the hard metal material, and thus it is possible toheighten abrasion resistance of the probe tip of each contactor andimprove durability of each contactor.

Also, by using the photolithographic technique for formation of theprobe tip portion including the probe tip, a so-called dovetail couplingstructure may be applied to coupling between the probe tip portion andthe arm portion formed subsequently, and thus strong coupling may beobtained between both the portions.

As the hard metal material, rhodium or palladium-cobalt alloy may beused, and the metal material may be deposited by a plating technique.

The third step may be conducted by irradiation of laser beam to thefirst flexible synthetic resin layer and the sacrificial layer in astate where the upper surface of the arm portion under the sacrificiallayer is protected by a protective film.

As the protective film, the plated copper layer may be used, and theplated copper layer may be formed on the upper surface of the armportion prior to the second step.

In the fourth step, the same material as the metal material for the armportion may be deposited in the opening at a height position thatexceeds the height position of the sacrificial layer and that does notexceed the first flexible synthetic resin layer, and subsequently thesame material as the metal material for the conductive path may bedeposited in the opening on the base portion within the thicknessdimension of the first flexible synthetic resin layer. By depositing thesame material as the metal material for the arm portion in the opening,the base portion of the contactor is formed. Also, by depositing thesame material as the metal material for the conductive path in theopening, the connection boundary between the base portion of thecontactor and the conductive path made of a different metal materialfrom the metal material constituting the base portion can be locatedsubstantially within the first flexible synthetic resin layer, and theconnection boundary between both the metals can be protected by thefirst flexible synthetic resin layer.

In the fifth step, a first conductive material, a second conductivematerial having higher toughness than that of the first conductivematerial, and the first conductive material for the conductive path maybe sequentially laminated on the first flexible synthetic resin layer.Thus, the conductive path may be in a three-layered structure, and thestrength of the conductive path against breakage may be heightened.

The first conductive material may be copper, and the second conductivematerial may be nickel or its alloy. These may be sequentially depositedon the first flexible resin by a plating technique.

In the fifth step, after formation of the conductive path, a reinforcingplate covering the upper region of the contactor may be fixed over thefirst flexible synthetic resin layer and the conductive path via anadhesive sheet. The arrangement of the reinforcing plate restrictsdeformation by an external force or deformation by thermal expansion orcontraction on the contactor area provided with the contactors of theprobe sheet main body and restricts displacement in the probe tippositions of the contactors caused by these deformations.

In a sixth step, a second flexible synthetic resin layer covering theconductive path formed on the first flexible synthetic resin layer maybe formed. By locating the conductive path between the second and firstflexible synthetic resin layers as a result of formation of this secondflexible resin layer, the conductive path may be buried in the syntheticresin film consisting of both the flexible synthetic resin layers.

In a seventh step, a sacrificial layer may be formed on the secondflexible synthetic resin layer, an opening reaching the conductive pathvia the second flexible synthetic resin layer and the sacrificial layerformed on the second flexible synthetic resin layer may be formed, and ametal material may be deposited in the opening. By this deposition ofthe metal material, a bump for the conductive path can be formed.

In an eighth step, the surface of the bump may be abraded to correspondto the surface of the sacrificial layer on the second flexible syntheticresin layer, and thus the respective electrical connections between theprobe sheet and e.g., the rigid wiring board to which the probe sheet isconnected can be done reliably. Also, after the aforementioned abrasionof the bump surface, the probe sheet main body may be detached from thebase table integrally with the contactor, and thereafter eachsacrificial layer remaining on the probe sheet may be removed.

Further, in a ninth step, by arranging the outer shape of the probesheet main body formed by burying the conductive path in the first andsecond flexible synthetic resin layers, sequential steps from formationof the probe tip to arrangement of the outer shape of the probe sheetmain body for completion of the probe sheet can be performed by acontinuous operation.

According to an embodiment of the present invention, the pluralcontactors formed at predetermined positions on the base table are notseparated individually, but the probe sheet main body to be coupled withthe base portion of each contactor is formed on the base table in astate where the probe tips of these contactors are held at predeterminedpositions on the base table, and thereafter, the contactor is separatedfrom the base table integrally with the probe sheet main body. Thus,conventional operations to couple the individual contactors with theprobe sheet main body are not needed. Also, troublesome positionaladjustment operations of the probe tips of the contactors in associationwith these conventional coupling operations are not needed. Accordingly,the probe sheet on which the probe tip of each contactor is arranged toalign in the same plane accurately at a predetermined position can bemanufactured more easily than in the conventional case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a probe assembly in which aflexible wiring board according to an embodiment of the presentinvention has been incorporated.

FIG. 2 is a vertical cross-sectional view of the probe assembly shown inFIG. 1.

FIG. 3 is a partially enlarged bottom view of a probe sheet of the probeassembly shown in FIG. 1.

FIG. 4 is a vertical cross-sectional view showing a state before theprobe sheet and a support block shown in FIG. 1 are coupled.

FIG. 5 is a partially enlarged vertical cross-sectional view showing astate after the probe sheet and the support block shown in FIG. 4 havebeen coupled.

FIG. 6 is a process description diagram (No. 1) showing a process formanufacturing the probe sheet according to an embodiment of the presentinvention.

FIG. 7 is a process description diagram (No. 2) showing a process formanufacturing the probe sheet according to an embodiment of the presentinvention.

FIG. 8 is a process description diagram (No. 3) showing a process formanufacturing the probe sheet according to an embodiment of the presentinvention.

FIG. 9 is a process description diagram (No. 4) showing a process formanufacturing the probe sheet according to an embodiment of the presentinvention.

FIG. 10 is a process description diagram (No. 5) showing a process formanufacturing the probe sheet according to an embodiment of the presentinvention.

FIG. 11 is a plan view of the probe sheet according to an embodiment ofthe present invention.

FIG. 12 is a perspective view of the probe tip of a probe according toan embodiment of the present invention seen from its tip end side.

FIG. 13 is a cross-sectional view obtained along the line XIII-XIIIshown in FIG. 12.

REFERENCE KEY

-   -   10 probe assembly    -   12 rigid wiring board    -   14 spring member    -   16 block    -   18 probe sheet main body (flexible wiring board)    -   18 a conductive path    -   20 probe sheet    -   48 contactor (probe)    -   48 a probe tip of the contactor    -   48 b arm portion of the contactor    -   48 c base portion of the contactor    -   50 contactor area    -   62, 64 electrical insulating synthetic resin film    -   66 first conductive material layer    -   68 second conductive material layer    -   70 plate-shaped member (ceramic plate)    -   100 base table    -   102 recess    -   116 copper layer (protective layer)    -   130 opening

DETAILED DESCRIPTION

A probe assembly 10 according to an embodiment of the present inventioncomprises a rigid wiring board 12, a block 16 elastically supported onthe rigid wiring board via a spring member 14, and a probe sheet 20having a flexible wiring board 18 provided with a plurality ofconductive paths 18 a (refer to FIG. 4) electrically connectedrespectively to a plurality of not shown wiring paths on the rigidwiring board 12, as shown in FIG. 1, which shows this in an explodedmanner. In the present embodiment, the flexible wiring board 18 is usedas a probe sheet main body of the probe sheet 20.

The rigid wiring board 12 has a plate-shaped electrical insulating basematerial made of epoxy resin containing e.g., glass fiber and wiringpaths on the base material, as is well known as a conventional rigidprinted wiring board. The aforementioned wiring paths on the rigidwiring board 12 are connected to electrical circuits of a not showntester main body. In the example shown in the figures, a circular rigidwiring board having a circular opening 12 a at the center is used as therigid wiring board 12.

The spring member 14 is made of a plate-shaped spring material andcomprises an annular support portion 14 a having a smaller outerdiameter than a diameter of the circular opening 12 a of the rigidwiring board 12 and a crosshair main body portion 14 b arranged acrossthe inside of the annular support portion.

On the upper surface of the rigid wiring board 12 is fixed a circularsupport plate 24 made of a metal such as stainless steel via bolts 22screwed in the rigid wiring board 12 at parts not in the way of theaforementioned wiring paths, as shown in FIG. 2. The support plate 24supports the rigid wiring board 12 and exerts a reinforcement effect onthe rigid wiring board.

The spring member 14 is held in the circular opening 12 a via an annularattachment plate 26 and a plurality of thrusting plates 28 annularlycombined to one another sandwiching its annular support portion 14 afrom its both sides. For holding of this spring member 14, theattachment plate 26 is coupled on the lower surface of the support plate24 by bolts 30, and each thrusting plate 28 is coupled with theattachment plate 26 by bolts 32 passing through the thrusting plate andthe aforementioned support portion 14 a of the spring member 14 andscrewed in the attachment plate 26. In this manner, the spring member 14is held in the circular opening 12 a to go across the opening.

Also, as shown in FIG. 2, a parallelism adjustment screw member 34 foradjusting the holding posture of the spring member 14 in a state inwhich the bolts 30 are loosened is screwed in the support plate 24 sothat its tip end can abut to the top surface of the attachment plate 26.

The aforementioned block 16 is fixed at the main body portion 14 b ofthe spring member 14 held in the circular opening 12 a of the rigidwiring board 12. The block 16 comprises a stem portion 16 a having arectangular cross-section and a support portion 16 b connected to thelower edge of the stem portion and having an equilateral octagonalcross-sectional shape in the example shown in the figures. The supportportion 16 b has a pedestal portion 36 having a predetermined diameteralong its axis line and a bottom portion 38 connected to the pedestalportion and having a cross-sectional shape analogous to thecross-sectional shape of the pedestal portion. The bottom portion 38gradually decreases toward the lower edge its lateral dimension or itsdiameter across the axis line of the support portion 16 b. Accordingly,the block 16 has tapered surfaces 40 at its bottom portion 38, and eightflat tapered surfaces 40 (refer to FIG. 3) are formed in the exampleshown in the figures.

Referring to FIG. 2 again, the block 16 is coupled with the main bodyportion 14 b of the spring member 14 at the top surface of the stemportion 16 a with the bottom portion 38 of its pedestal portion 36directing downward. For this coupling, a fixing plate 42 sandwiching themain body portion 14 b in cooperation with the stem portion 16 a isfixed to the stem portion 16 a by screw members 44 screwed in the stemportion 16 a.

Also, the flexible wiring board 18 or the probe sheet main body 18 ofthe probe sheet 20 has an octagonal portion 46 formed at its centerportion to correspond to the bottom portion 38 of the block 16, and atthe center portion of the octagonal portion is formed a contactor area50 at which numerous probes 48 are arranged with their probe tips 48 aarrayed, as shown in FIG. 3. This contactor area 50 is formed in arectangular shape in the example shown in FIG. 3.

The probe sheet 20 is attached to the lower surface of the bottomportion 38 via adhesive as described later, with the probe tips 48 a ofthe numerous probes 48 protruded from the contactor area 50 of its probesheet main body 18 directing downward, so that the octagonal portion 46is supported on the bottom portion 38 of the block 16 at its backsurface, as shown in FIG. 2. Also, as for the probe sheet 20, its outeredge portions are coupled with the rigid wiring board 12 so thatportions extending outward from the octagonal portion 46 are slightlyslack. For coupling of the aforementioned outer edge portions of theprobe sheet 20, an elastic rubber ring 52 is arranged along the outeredge portions of the probe sheet 20, and a ring bracket 54 covering theelastic rubber ring 52 is also arranged. The relative positions of theouter edge portions of the probe sheet 20 and both the members 52, 54against the rigid wiring board 12 are determined by positioning pins 56.By tightening of screw members 58 passing through the probe sheet 20 andboth the members 52, 54 into the rigid wiring board 12, the outer edgeportions of the probe sheet 20 are coupled with the rigid wiring board12. By coupling of the aforementioned outer edge portions with the rigidwiring board 12, the aforementioned conductive paths 18 a in the probesheet 20 are electrically connected to the aforementioned correspondingwiring paths on the rigid wiring board 12, as in the conventional case.

In the example shown in FIGS. 2 and 3, alignment pins 60 are arranged topass through elongated holes 60 a (refer to FIG. 3) provided in theprobe sheet 20. The lower edges of the alignment pins 60 are providedwith alignment marks 60 b that can be captured by a camera supported ona table (not shown).

Since relative positional information of the probe assembly 10 to thetable supporting a device under test can be obtained from capturedimages of these alignment marks, the relative position of the probeassembly 10 to the aforementioned support table is adjusted based onthis positional information so that the probe tips 48 a of therespective probes 48 of the probe assembly 10 contact correspondingelectrodes of the device under test on the aforementioned tableaccurately. Thereafter, as a result of the electrical contact betweenthe probe tips 48 a of the respective probes 48 and the aforementionedcorresponding electrodes, an electrical test of the aforementioneddevice under test is performed in the aforementioned tester main body.

The structure of the aforementioned probe sheet 20 is described indetails with reference to FIG. 4. The probe sheet 20 has a pair offlexible electrical insulating synthetic resin films 62, 64 such aspolyimide resin, and the conductive paths 18 a are buried between boththe resin films.

In the probe assembly 10 according to an embodiment of the presentinvention, the conductive path 18 a has a laminated structure havingfirst conductive material layers 66 made of a metal material, such ascopper, having high conductivity suitable for use as an electrical wireand a second conductive material layer 68 made of a metal material, suchas nickel or nickel-phosphor alloy, having higher toughness than that ofthe first conductive material layers. The example shown in FIG. 4 adoptsa three-layered sandwich structure in which a single second conductivematerial layer 68 is sandwiched between a pair of first conductivematerial layers 66.

The resiliencies of the two kinds of metals can be compared by derivingrespective stress-strain curves of both the metals having the sameshapes and dimensions from e.g., impact tests, and comparing the areaseach bounded by each of the stress-strain curves extending to a pointwhere each of these metals reaches breakage. In the case of comparisonbetween copper and nickel, the area bounded by the stress-strain curvederived from nickel is larger than that derived from copper. Thus, itcan be said that nickel is a material harder to be broken than copper,that is, a highly tough material.

Since each of both the first conductive material layers 66 is depositedto have a thickness of e.g., 10 micrometers, and the second conductivematerial layer 68 is deposited to have a thickness of e.g., 2micrometers, the conductive path 18 a has a thickness dimension of e.g.,approximately 22 micrometers. These metal layers 66, 68 may be depositedby an electroplating method as described later.

To each conductive path 18 a is connected the base portion of the probe48 protruded from one electrical insulating synthetic resin film 62.Also, corresponding to the contactor area 50 (refer to FIG. 3) to whicheach probe 48 is arranged, a plate-shaped reinforcing plate 70 made of,for example, a ceramic plate having approximately the same size andshape as those of the contactor area is buried between both theelectrical insulating synthetic resin films 62, 64 to partially coverthe conductive paths 18 a. This reinforcing plate 70 can be fixedbetween both the electrical insulating synthetic resin films 62, 64 viaan adhesive sheet 72 such as a synthetic resin sheet, as shown in thefigure. Since the reinforcing plate 70 has higher rigidity than that ofthe electrical insulating synthetic resin films 62, 64, it acts torestrict deformation of an area of the probe sheet main body 18corresponding to the reinforcing plate 70 by an external force.

Although another plate-shaped member may be used as the reinforcingplate, a ceramic plate may be used because it is light and less likelysuffers from thermal deformation. Since the reinforcing plate 70 made ofthe ceramic plate less likely suffers from deformation by thermalexpansion or contraction, it effectively restricts deformation of theprobe sheet main body 18 by thermal expansion or contraction as well asthe aforementioned deformation of the probe sheet main body 18 by anexternal force.

The aforementioned reinforcing plate 70 is arranged between theelectrical insulating synthetic resin films 62, 64 on a side of eachconductive path 18 a opposite a side provided with a connection portionbetween the conductive path and each probe 48 as a contactor. Thisarrangement enables the reinforcing plate 70 to be arranged to cover theentire area of the contactor area 50 without the need for any specialgeometric process to the single plate-shaped member 70 for prevention ofinterference with each probe 48 or contactor 48.

Also, by burying the reinforcing plate 70, a protrusion 74 correspondingto the reinforcing plate 70 is formed in the other electrical insulatingsynthetic resin film 64 forming the back surface of the probe sheet mainbody 18 in a state prior to fixation of the probe sheet main body 18 ofthe probe sheet 20 to the block 16, as shown in FIG. 4. On the otherhand, no such protrusion corresponding to the reinforcing plate 70 isformed in the electrical insulating synthetic resin film 62 forming thefront surface of the probe sheet main body 18.

On the lower surface of the bottom portion 38 of the block 16 receivingthe back surface of the probe sheet main body 18 is formed a flatrectangular support surface 76 corresponding approximately to thecontactor area 50 as shown in FIG. 4. This support surface 76 is formedat the center part of the bottom portion 38, and an octagonal flat step78 surrounding the center part causes the support surface 76 to beformed so as to be protruded downward from the step. Thus, the taperedsurfaces 40 communicate with the support surface 76 via the step 78between the tapered surfaces and the support surface 76.

In the support surface 76 formed to be protruded downward from the flatstep 78 is opened downward a rectangular center recess 80 for housingadhesive 80 a. The center recess 80 is formed in a slightly smaller flatsurface shape than that of the contactor area 50. As a result offormation of the center recess 80, an annular flat support surface part76 a surrounding the center recess 80 remains on the support surface 76.The support surface part 76 a is formed to have a size appropriate toreceiving the edge portion of the reinforcing plate 70, and in thesupport surface part 76 a is formed an annular groove 82 surrounding therecess 80.

For attachment of the probe sheet 20 to the block 16, the adhesive 80 ais supplied to the center recess 80. Also, similar adhesive is suppliedto the step 78 surrounding the support surface 76 as well.

After the aforementioned supply of the adhesive to the block 16, therelative position between the probe sheet 20 and the block 16 isdetermined so that the outer edge portion of the protrusion 74 of theprobe sheet main body 18 is opposed to the support surface part 76 a asshown in FIG. 4. Under this state, the probe sheet main body 18 isthrust toward the lower surface of the bottom portion 38 of the block 16as shown in FIG. 5.

As a result of this thrust, the protrusion 74 of the probe sheet mainbody 18 disappears, and on the contrary the probe sheet main body 18 isdeformed to be in a recessed shape so that its back surface extendsalong the step 78 and the support surface 76, which causes the probesheet main body 18 to be fixed on the support surface 76 and the step 78as the lower surface of the bottom portion 38 (except the taperedsurfaces 40).

Also, when the back surface of the probe sheet main body 18 is deformedto extend along the step 78 and the support surface 76, the probe sheetmain body 18 is deformed entirely in its thickness direction. At thismoment, at an area corresponding to the outer edge of the supportsurface 76, a strong shearing stress acts on the conductive paths 18 adue to the step difference between the support surface and the step 78.

However, with the probe sheet 20 according to an embodiment of thepresent invention, since its conductive paths 18 a are reinforced by thesecond conductive material layers 68 showing high toughness, theconductive paths 18 a will not be broken by such a shearing force. Also,the reinforcement effect of the second conductive material layers 68 mayprevent breakage of the conductive paths 18 a reliably in anafter-mentioned process for manufacturing the probe sheet 20 as well.

In the aforementioned attachment work of the probe sheet main body 18 tothe block 16, since the excess of the adhesive 80 a supplied to therecess 80 is housed in the annular groove 82 when the probe sheet mainbody 18 receives the aforementioned thrusting force, this excess willnot go over the support surface part 76 a and run off into the step 78.

Also, as a result of the aforementioned thrust of the probe sheet mainbody 18 to the block 16, the sum of the step difference between the step78 and the support surface 76 and the thickness of the reinforcing plate70 appears as a step difference ΔH of the surface of the probe sheetmain body 18 at the same time of the aforementioned disappearance of theprotrusion 74. Consequently, the contactor area 50 of the probe sheetmain body 18 is protruded downward from its circumferential portion bythe step difference ΔH.

This step difference ΔH may contribute to increase of the distancebetween the outward part of the contactor area 50 of the probe sheetmain body 18 and the aforementioned device under test. This increase ofthe distance prevents interference between the outward part of thecontactor area 50 of the probe sheet main body 18 and the aforementioneddevice under test more reliably and prevents contamination or damage ofthe aforementioned device under test caused by the interference of boththe parts more reliably.

Even in a case where the reinforcing plate 70 is not used, the supportsurface 76 may be protruded from its circumferential part to obtain astep difference ΔH corresponding to the protrusion of the supportsurface 76. However, it is preferable to use the reinforcing plate 70since doing so will lead to obtaining of a larger step difference ΔH,easy handling of the probe sheet 20, and prevention of misalignment ofthe probe tips 48 a of the probes 48 on the xy plain and misalignmentwith respect to the position in the z direction as a height position ofeach probe tip.

For example, at the time of manufacturing of the probe sheet 20, howeverwell the probe tips 48 a of the probes 48 are aligned, the alignedposture of each probe 48 is misaligned when deformation by an externalforce or deformation by thermal expansion or contraction occurs on thecontactor area 50 during handling of it, as a result of which thealignment of the probe tips 48 a is misaligned. Also, when the contactorarea 50 is deflected at the time of being attached to the block 16, andthe probe sheet main body 18 is fixed to the support surface 76 in astate where this deflection remains, the alignment of the probe tips 48a is misaligned in a similar manner.

However, by burying the reinforcing plate 70 corresponding to thecontactor area 50 of the probe sheet main body 18 in the probe sheetmain body 18, the aforementioned deformation on the contactor area 50 ofthe probe sheet main body can be prevented reliably. Thus, themisalignment of the posture of each probe or contactor 48 caused bydeformation of the contactor area 50 may be prevented, and themisalignment of the probe tip 48 a of this contactor 48 may be preventedreliably. This leads to easy handling of the probe sheet 20 and providesa probe assembly 10 with the probe tips 48 a having high positionalaccuracy.

Next, a method for manufacturing the probe sheet 20 according to anembodiment of the present invention is described with reference to FIGS.6 to 13. For simplification of description and drawings, the followingembodiment is described in terms of a single probe representing aplurality of contactors or probes formed at the same time.

First Step

In the method for manufacturing the probe sheet according to anembodiment of the present invention, a metal plate such as a stainlesssteel plate is used as a base table 100, and on its surface is formed ahitting mark by, for example, an indenter to form a recess 102 for theprobe tip of the probe 48, as shown in FIG. 6 (a). Meanwhile, although asingle recess 102 is shown in the figure, as many recesses 102 as thenumber of the probes 48 to be formed on the aforementioned contactorarea 50 are formed with a predetermined probe tip pitch, as is apparentfrom the above description.

After formation of the recess 102, a pattern mask 104 that takes theform of the probe tip 48 a of the probe 48 is formed at an areaincluding the recess 102 by selective exposure and developmentprocessing with photoresist with use of a photolithographic technique(FIG. 6 (b)).

With use of this pattern mask 104, a metal 106 for the probe tip 48 a isdeposited in and around the recess 102 by, for example, electroplating(FIG. 6 (c)). As a metal material for the probe tip 48 a, a hard metalsuch as rhodium or palladium-cobalt alloy is used. After deposition ofthe metal 106, the pattern mask 104 is removed (FIG. 6 (d)).

After removal of the pattern mask 104, a pattern mask 108 for asacrificial layer to be removed after completion of the probe sheet 20is formed on the base table 100 with photoresist with use of theaforementioned photolithographic technique, as shown in FIG. 6 (e).

For the aforementioned sacrificial layer, a nickel layer 110 is firstdeposited at an area where the base table 100 is exposed from thepattern mask 108 by, for example, a plating technique. Subsequently, acopper layer 112 is deposited on the nickel layer 110 by a similarplating technique. On the base table 100, a metal material for formingan arm portion 48 b as a main body of the probe 48 will be depositedlater on, and the copper layer 112 functions to make it easy to detachthe probe main body formed by the deposition of the metal material fromthe base table 100. Also, the copper layer 112 is deposited over thebase table 100 via the nickel layer 110 because it may be difficult todeposit the copper layer 112 directly on the base table 100.

After formation of the aforementioned sacrificial layers 110, 112, thepattern mask 108 is removed (FIG. 6 (g)). Thereafter, a pattern mask 114for the arm portion, continuing into the probe tip 48 a, of the probe 48is formed with photoresist similar to one described above (FIG. 6 (h)).In an area exposed from the pattern mask 114, a metal material for thearm portion of the probe 48 is deposited on the metal 106 for the probetip 48 a and the sacrificial layers 110, 112 by a plating technique suchas an electroforming technique. In this manner, the arm portion 48 b isformed integrally with the probe tip 48 a that is the metal 106 (FIG. 6(i)). As a metal material for the arm portion 48 b, a nickel-phosphoralloy is used, for example.

In a state where the pattern mask 114 remains, a copper layer 116 thatfunctions as a protective film in an after-mentioned process is formedon the arm portion 48 b by, for example, a plating technique (FIG. 6(j)). After formation of this copper layer 116, the pattern mask 114 isremoved (FIG. 6 (k)).

After formation of the arm portion 48 b, a second sacrificial layer thatwill be a reference plane of the probe sheet main body 18 is formed.Prior to formation of this second sacrificial layer, a pattern mask 118,made of photoresist, selectively covering the arm portion 48 b withwhich the probe tip 48 a has been formed integrally on the base table100 is formed by a photoresist technique similar to one described above(FIG. 7 (a)). At an area exposed from the pattern mask 118 over the basetable 100 is deposited a metal material for a second sacrificial layer120 (FIG. 7 (b)). Nickel may be used as a material for the secondsacrificial layer 120 and may be deposited by a plating technique.

After formation of the second sacrificial layer 120, the pattern mask118 covering the arm portion 48 b is removed (FIG. 7 (c)). Thereafter, aresist mask 122 made of photoresist for partially removing the copperlayer 116 on the arm portion 48 b is formed entirely over the base table100 with only an unnecessary part of the protective film that is thecopper layer 116 exposed (FIG. 7 (d)).

When the unnecessary part of the copper layer 116 exposed from theresist mask 122 is removed by etching (FIG. 7 (e)), the resist mask 122is removed (FIG. 7 (f)). This removal of the unnecessary part of thecopper layer 116 prevents the elasticity of the arm portion 48 b withflexible deformation from being impaired by the copper layer 116. Thus,predetermined elasticity of the probe 48 is maintained.

Second Step

After exposure of the second sacrificial layer 120 as a reference planeof the probe sheet main body 18 and the arm portion 48 b on the basetable 100 by removal of the resist mask 122, on these are sequentiallyformed a dry film 124 that is a third sacrificial layer, a resin layer126 for the first electrical insulating synthetic resin film 62 of theprobe sheet main body 18, and a protective film 128 made of resist (FIG.7 (g)).

Third Step

In a state where the surface of the resin layer 126 or the electricalinsulating synthetic resin film 62 is protected by the protective film128, an opening 130 reaching the copper layer 116 on the arm portion 48b is formed by using, for example, laser beam (FIG. 7 (h)). The loweredge of this opening 130 is an edge portion of the arm portion 48 blocated opposite the probe tip 48 a and is opened on the copper layer116. This copper layer 116 covers the upper surface of the arm portion48 b to protect the arm portion from the laser beam.

Fourth Step

After formation of the opening 130, the copper layer 116 in the opening130 is removed by etching, and the arm portion 48 b is exposed in theopening 130 (FIG. 7 (i)). In the opening 130 is deposited, for example,a nickel layer 132 for forming a base portion 48 c of the probe 48 by aplating technique on the arm portion 48 b to be integral with it. Thethickness dimension of the nickel layer 132 in the opening 130 exceedsthe thickness dimension of the dry film or the third sacrificial layer124 but will not exceed the sum of the thickness dimensions of thesacrificial layer and the resin layer 126. Thus, the upper surface ofthe nickel layer 132 is located within the thickness region of the resinlayer 126 for the electrical insulating synthetic resin film 62.

On the upper surface of the nickel layer 132 is deposited a copper layer134 by a plating technique so as to be integrated with the nickel layer132. Thus, the dissimilar metal joint area of these both metals 132, 134exists within the thickness range of the resin layer 126 or theelectrical insulating synthetic resin film 62. The aforementioneddissimilar metal joint area is hereby protected by the electricalinsulating synthetic resin film 62. The copper layer 134 has a thicknessdimension enough for its upper surface to approximately correspond tothe upper surface of the resin layer 126. After deposition of the copperlayer 134, the protective film 128 is removed (FIG. 7 (k)).

Fifth Step

On the resin layer 126 and the copper layer 134 exposed as a result ofremoval of the protective film 128 is formed a copper layer 136 having athickness dimension of, for example, 0.3 μm for growing the conductivepath 18 a by sputtering, as shown in FIG. 8 (a).

Thereafter, as shown in FIG. 8 (b), a pattern mask 138 taking the formof the conductive path area including the upper portion of the copperlayer 134 is formed with photoresist by a photolithographic technique.In an area exposed from the pattern mask 138 are sequentially depositeda copper layer 66 having a thickness dimension of 10 μm, a nickel layer68 having a thickness dimension of 2 μm, and a copper layer 66 having athickness dimension of 10 μm for the conductive path 18 a by, forexample, a plating technique (FIG. 8 (c)).

After the conductive path 18 a is formed as a result of deposition ofthe copper layer 66, the nickel layer 68, and the copper layer 66, thepattern mask 138 is removed (FIG. 8 (d)), and a part of the copper layer136 running off from the conductive path 18 a is removed by etching(FIG. 8 (e)).

In this manner, the conductive path 18 a excellent in strength againstbreakage can be formed as described above.

Sixth Step

On the resin layer 126 or the electrical insulating synthetic resin film62, exposed as a result of removal of the pattern mask 138 and partialremoval of the copper layer 136, and the conductive path 18 a on thefilm, an adhesive sheet 72 made of a synthetic resin material is bonded,and the ceramic plate 70 covering the contactor area 50 is arranged onthe sheet, as shown in FIG. 8 (f). Further, after a similar adhesivesheet 72 is arranged to cover the ceramic plate 70, a polyimide resinlayer 140 for forming the other electrical insulating synthetic resinfilm 64 is deposited to cover them, as shown in FIG. 8 (g).

At the time of formation of this polyimide resin layer 140, a thrustingforce F acts on the polyimide resin layer. Although part of thisthrusting force F acts as a shearing force to the conductive path 18 aat a part shown by a reference numeral 142 that is an edge portion ofthe base portion 48 c of the probe 48 formed by deposition of the nickellayer 132 and the copper layer 134, the conductive path 18 a, which hasbeen reinforced by the second conductive material layer 68, will not bedamaged by this shearing force.

Seventh Step

After formation of the polyimide resin layer 140, a dry film 144 isbonded on the polyimide resin layer as a fourth sacrificial layer (FIG.9 (a)). Thereafter, as shown in FIG. 9 (b), an opening 146 opened on theconductive path 18 a via the fourth sacrificial layer 144 and theunderlying polyimide resin layer 140 is formed by laser beam.

In this opening 146 is deposited a metal material for a pad or a bump148 by plating, as shown in FIG. 9 (c). As a metal material for the bump148, nickel may be deposited, for example.

Eighth Step

A part of the bump 148 protruded from the surface of the fourthsacrificial layer 144 undergoes an abrasion process so as to be flat(FIG. 9 (d)), and on this flat surface is formed a gold layer 150 forfavorable electrical contact with the aforementioned wiring path of theaforementioned rigid wiring board 12 by, for example, a platingtechnique.

After formation of the gold layer 150, the probe sheet main body 18 isremoved from the base table 100 together with the second sacrificiallayer 120, the fourth sacrificial layer 144, and so on, as shown in FIG.10 (a). At this moment, even if a part of the detaching force acts as abending force on the contactor area 50 of the probe sheet main body 18via the probes 48, deformation of the contactor area 50 is restricted bythe reinforcing plate 70 buried inside the contactor area 50.

Accordingly, displacement of the posture of each probe 48 and the probetip 48 a caused by this detachment is prevented.

After removal of the base table 100 as a result of detachment of theprobe 48, the aforementioned first sacrificial layer consisting of thenickel layer 110 and the copper layer 112 and the second sacrificiallayer 120 are respectively removed by an etching process (FIG. 10 (b)).Also, the dry film 124 exposed as a result of removal of the secondsacrificial layer 120 is removed, and further the fourth sacrificiallayer 144 is removed (FIG. 10 (c)).

Ninth Step

Thereafter, as shown in FIG. 11, the outline of the probe sheet mainbody 18 is set by a laser process or a cutting process by means of acutter, and openings 56 a that receive the positioning pins 56 and theelongated holes 60 a that receive the alignment pins 60 are respectivelyformed at locations that are not in the way of the conductive paths 18 aof the probe sheet main body 18, thus to form the probe assembly 10.

With the aforementioned method for manufacturing the probe sheet 20according to an embodiment of the present invention, the probe tip 48 a,the arm portion 48 b, and the base portion 48 c of each probe 48required to have extremely high accuracy are sequentially formed on thebase table 100. Also, in a state where each probe 48 is held on the basetable 100, the probe sheet main body 18 to be coupled with this probe 48is formed integrally with the probe 48.

Accordingly, since operations to couple the probes or the contactors 48with the probe sheet main body 18 individually are not needed, andassociated positional adjustment operations of the probe tips 48 a ofthe contactors 48 are not needed, the probe sheet 20 on which the probetip 48 a of each contactor 48 is arranged accurately at a predeterminedposition can be manufactured more easily than in the conventional case.Also, sequential steps from formation of the probe tip 48 a toarrangement of the outer shape of the probe sheet main body 18 forcompletion of the probe sheet 20 can be performed efficiently by acontinuous operation.

Also, in the first step for forming the probe tip 48 a and the armportion 48 b of the contactor 48, prior to deposition of the metalmaterial for the arm portion 48 b on the base table 100, a harder metalmaterial than the metal material for the arm portion 48 b can bedeposited in the recess 102 of the base table 100. After deposition ofthis hard metal material, the metal material for the arm portion 48 b isdeposited to cover the metal material to enable to form the probe tip 48a of each contactor 48 with the hard metal material, and thus it ispossible to heighten abrasion resistance of the probe tip 48 a of eachcontactor 48 and improve durability of each contactor 48.

In this first step, the photolithographic technique may be used forformation of the probe tip 48 a as described above. By using thisphotolithographic technique, a skirt portion 48 d whose width dimensionincreases toward the end surface in accordance with the end surfaceshape of the edge portion of the pattern mask 104 is formed at both edgeportions of the probe tip 48 a made of the metal 106, as shown in FIGS.12 and 13. Since the arm portion 48 b is formed by deposition of themetal material so as to cover this skirt portion 48 d, so-calleddovetail coupling is made at the coupling portion between the probe tip48 a and the arm portion 48 b. Consequently, strong coupling may beobtained between both the portions 48 b and 48 d.

Also, in the aforementioned fourth step, the same material as the armportion 48 b is deposited in the opening 130 for the base portion 48 cat a height position that exceeds the height position of the sacrificiallayer that is the dry film 124 and that does not exceed the firstflexible synthetic resin layer 126. Thereafter, copper, which is thesame material as a metal material for the conductive path 18 a isdeposited on the base portion 48 b in the opening 130 within thethickness dimension of the first flexible synthetic resin layer 126. Asa result, since the connection boundary between the base portion 48 c ofthe contactor 48 and the conductive path 18 a made of a different metalmaterial from the base portion may be located substantially within thefirst flexible synthetic resin layer 126 (62), the connection boundarybetween both the metals may be protected by the first flexible syntheticresin layer 126 (62).

In the fifth step for forming the conductive path 18 a, the firstconductive material layer 66, the second conductive material layer 68having higher toughness than the first conductive material layer, andthe aforementioned first conductive material layer 66 for the conductivepath 18 a may be deposited sequentially on the first flexible syntheticresin layer 126 (62). Thus, the conductive path 18 a may be in athree-layered structure, and the strength of the conductive path 18 aagainst breakage can be heightened.

Also, in this fifth step, after formation of the conductive path 18 a,the reinforcing plate 70 covering the upper region of the contactor 48may be fixed over the first flexible synthetic resin layer 126 (62) andthe conductive path 18 a via the adhesive sheet 72. The arrangement ofthe reinforcing plate 70 may restrict deformation by an external forceor deformation by thermal expansion or contraction on the contactor area50 provided with the respective contactors 48 at the time of detachmentof the contactors 48 of the probe sheet main body 18 from the base table100 in the process of forming the probe sheet 20 or in handling of theprobe sheet main body 18 in attachment of the probe sheet 20 to theblock 16 or the rigid wiring board 12 etc. and can restrict displacementin the probe tip positions of the contactors caused by thesedeformations, as described above.

The present invention is not limited to the above embodiments but may bealtered in various ways without departing from the spirit and scope ofthe present invention.

1. A method for manufacturing a probe sheet comprising a probe sheetmain body having a flexible insulating synthetic resin film andconductive paths supported by said synthetic resin film and a pluralityof contactors formed to be protruded from one surface of said probesheet main body and connected to said conductive paths, comprising: afirst step of forming photoresist taking the form of each probe tip andeach arm portion continuing into said probe tip on a base table havingformed therein a recess for said probe tip of each contactor with use ofa photolithographic technique and forming said probe tip and said armportion of said contactor by depositing a metal material in said recessformed in said photoresist; a second step of, after removal of saidphotoresist, forming a sacrificial layer on the end portion of said armportion and forming a first flexible synthetic resin layer for saidprobe sheet main body on said sacrificial layer; a third step of formingan opening reaching said arm portion via said flexible synthetic resinlayer and said sacrificial layer; a fourth step of forming a baseportion continuing into said arm portion of said contactor by depositinga metal material in said opening; and a fifth step of forming on saidflexible synthetic resin layer photoresist taking the form of aconductive path passing on said base portion formed in said opening withuse of a photolithographic technique and forming on said synthetic resinlayer said conductive path coupled with said base portion by depositinga metal material in a recess formed in said photoresist, wherein saidcontactors are separated from said base table integrally with said probesheet main body.
 2. The manufacturing method according to claim 1,wherein said base table comprises a stainless steel plate, said metalmaterial for said contactor is nickel or its alloy, and said first stepincludes the step of, prior to deposition of said metal material forsaid arm portion on said base table, sequentially laminating a nickellayer for promoting growth of a copper layer on said base table for easydetachment of said arm portion from said base table and said copperlayer on said nickel layer and depositing said metal material forformation of said arm portion on said base table via said both layers.3. The manufacturing method according to claim 2, wherein deposition ofsaid metal material for said arm portion and lamination of said nickellayer and said copper layer are respectively conducted by a platingtechnique.
 4. The manufacturing method according to claim 1, whereinsaid first step includes the step of, prior to deposition of said metalmaterial for said arm portion on said base table, depositing a hardermetal material than said metal material for said arm portion in saidrecess on said base table, and after deposition of said metal material,depositing said metal material for said arm portion to cover said metalmaterial.
 5. The manufacturing method according to claim 4, wherein saidhard metal material is rhodium or palladium-cobalt alloy, and said metalmaterial is deposited by a plating technique.
 6. The manufacturingmethod according to claim 1, wherein said third step is conducted byirradiation of laser beam to said first flexible synthetic resin layerand said sacrificial layer in a state where the upper surface of saidarm portion under said sacrificial layer is protected by a protectivefilm.
 7. The manufacturing method according to claim 6, wherein saidprotective film is a plated copper layer formed on the upper surface ofsaid arm portion prior to said second step.
 8. The manufacturing methodaccording to claim 1, wherein said fourth step includes the step ofdepositing in said opening the same material as said metal material forsaid arm portion at a height position that exceeds the height positionof said sacrificial layer and that does not exceed said first flexiblesynthetic resin layer to form said base portion and subsequentlydepositing in said opening on said base portion the same material assaid metal material for said conductive path within the thicknessdimension of said first flexible synthetic resin layer.
 9. Themanufacturing method according to claim 1, wherein said fifth stepincludes the step of sequentially laminating a first conductivematerial, a second conductive material having higher toughness than thatof said first conductive material, and said first conductive materialfor said conductive path on said first flexible synthetic resin layer,thus to form said conductive path having a three-layered structure. 10.The manufacturing method according to claim 9, wherein said firstconductive material is copper, said second conductive material is nickelor its alloy, and these are sequentially deposited by a platingtechnique.
 11. The manufacturing method according to claim 1, whereinsaid fifth step includes the step of, after formation of said conductivepath, fixing a reinforcing plate covering the upper region of saidcontactor over said first flexible synthetic resin layer and saidconductive path via an adhesive sheet.
 12. The manufacturing methodaccording to claim 1, further comprising a sixth step of forming asecond flexible synthetic resin layer covering said conductive pathformed on said first flexible synthetic resin layer for the purpose ofburying said conductive path in cooperation with said first flexiblesynthetic resin layer.
 13. The manufacturing method according to claim12, further comprising a seventh step of forming a sacrificial layer onsaid second flexible synthetic resin layer, forming an opening reachingsaid conductive path via said second flexible synthetic resin layer andsaid sacrificial layer on said second flexible synthetic resin layer,and depositing a metal material in said opening, thus to form a bump forsaid conductive path and an eighth step of abrading the surface of saidbump to correspond to the surface of said sacrificial layer on saidsecond flexible synthetic resin layer, wherein, after detaching saidcontactor from said base table integrally with said probe sheet mainbody, said each sacrificial layer remaining on said probe sheet isremoved.
 14. The manufacturing method according to claim 13, furthercomprising a ninth step of arranging the outer shape of said probe sheetmain body formed by burying said conductive path in said first andsecond flexible synthetic resin layers.